Thursday, June 5, 2008
Break out the ARK
Looks like my former residence is going to be flooding again.
The ingredients for this years severe weather season have all come together perfectly. Moisture, dynamics, timing, and plenty of initiating mechanisms. Something is truly remarkable about this year compared to not only the last 3 years of ho hum seasons, but in general.
Things to look for are the areal average surface moisture bias and cape, the storm track and thus shear, and also the moisture depth. i am becoming increasingly convinced that moisture depth is just as important as variables such as cape. Doubt me? Look at the DVN sounding, which is pretty similar to the ILX sounding at the same time and the DV sounding 6 hours previous.
The bulk of the tornado's occurred downstream from these soundings. But, you say, OAX was also very similar. Well plenty of tor warned storms and plenty of mid level rotation in IA today. But the key: downdraft cape from the freezing level! OAX had a higher DCAPE but its freezing level environment was far dryer. This was an indication that the lid was "stronger" at OAX, or at the very least lower to the ground.
The variable combinations for severe weather are so hard to pick off. But I think "low-level" shear, up to the max moisture depth is important. CAPE in the lower levels is important but indicative of the lower level moisture content. The DCAPE figures in as we include the effects of the lid and any downdraft generation. The downdraft and resulting outflow must be important to the gust front dynamics of these storms since the density gradient helps determine the speed of these features. if the supercell motion and the gust front motion match (a sort of critical level) tornados form (in some circumstances). I have yet to see a full paper dedicated to the structural characteristics of the tornado environment prior to and during tornadogenesis. The focus is always on the tornado and parent mesocyclone.
Someday I hope to work these concepts out. maybe the vortex guys will beat me to it. But they seam bent on understanding the tornado and not necessarily the whole storm in context. The DRC's helped expand the view a little. So did the owl horn signature.
Maybe the Sticknet program will break out some interesting results. RFD's are important. But how and where do they form, and are they common?